Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
The invention relates to an aerodynamic seal for continuous thermal treatment plants with a protective gas atmosphere, having slit nozzles which delimit an orifice cross section to be sealed off in the continuous thermal treatment plant and which are directed onto a metal strip running through.
In various industrial plants, it is necessary to have non-contact seals between two gas zones. Thus, the problem is either that gases or vapours occurring within a chamber should not pass into the outside atmosphere or that atmospheric air should not be introduced, for example, into a chamber to which protective gas is applied. The chamber should nevertheless be freely accessible, so that the contact-sensitive material to be treated can be supplied.
Continuous furnaces for sheet-metal strips, for example, have such a requirement. The thermal treatment of easily oxidizing metal sheets is carried out in the furnace under protective gas. On account of the surface sensitivity of the sheet-metal strips, however, mechanical sealing of the furnace orifice relative to the outside atmosphere should be avoided as far as possible.
In the instances mentioned above, therefore, aerodynamic seals are used, in which a gas jet separates the two gas zones from one another.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
DE-C-37 43 598 discloses an aerodynamic seal with a double slit nozzle. The nozzle has a middle partition which provides two nozzle spaces, into which the gas of the gas zones to be sealed off from one another is introduced in each case. The gas jet together with its two part-jets impinges with its core region onto an impact surface which is formed, for example, by the sheet-metal strip running into a continuous furnace. Since only slight turbulence prevails in the core region of the gas jet, intermixing of protective gas and air should be largely avoided.
The solution requires the double slit nozzle or nozzles to be positioned as near as possible to the surface of the strip running through, in order to achieve a good sealing effect. However, since strips of this type are never completely flat, but have bulges and corrugations and, at the run-through speeds reached, small strip movements also occur perpendicularly to the strip surface, this requirement cannot be fulfilled without further action. The double slit nozzles must therefore be arranged at a specific minimum distance from the strip running through and, for this purpose, have a corresponding slit width. Intermixings of air and protective gas may nevertheless occur, so that, on the one hand, protective gas losses arise and, on the other hand, air may penetrate into the furnace.
Furthermore, DE 44 41 690 A1 discloses an aerodynamic seal, for example for continuous furnaces. Here too, two gases emerging in parallel from a chamber divided in two form a gas curtain perpendicularly to a conveyor band. This version entails the abovementioned disadvantages of the seal from DE-C-37 43 598. It also proves a disadvantage, here, that the chamber outlet orifice is subdivided into tiny orifices by means of a perforated plate, thus causing a barrier gas jet to have a lower flow velocity. A barrier gas jet of this type is unsuitable for counteracting a flow pulse from a system operated with inert gas.
Moreover, DE-C-973 548 discloses a seal in the form of barrier air jets, which is used on rotating regenerative heat exchangers. In this case, hot smoke gas and cool air flowing in countercurrent to the latter are conducted next to one another through a rotor provided with heating plates. The smoke gas and air are separated by means of barrier air jets. The nozzles for this purpose are arranged between the smoke-gas region and the air region above and below the rotor. Barrier air is blown out of these nozzles through the rotor at high velocity, and this barrier air is subsequently sucked away again The barrier air jet generated in this way is unsuitable for strips, since, unlike a rotor provided with heating plates, a strip cannot be penetrated by a barrier air jet.
The object on which the invention is based is to specify an aerodynamic seal of the type mentioned in the introduction, by means of which the intermixing of the gases involved is further reduced.
The object is achieved, according to the invention, in that each side of the metal strip is assigned two separate slit nozzles which are arranged at a distance one behind the other in the run-through direction of the metal strip and each generate a gas jet directed perpendicularly onto the metal strip or, pointed away from one another, at an angle onto the metal strip and of which the slit nozzles directed onto the side of the atmosphere have air applied to them and the slit nozzles directed towards the side of the continuous thermal treatment plant have protective gas applied to them.